Temperature-responsive switch having self-contained heater



Oct.- 21, 1969 w. R. DAVENPORT ET AL 3,474,372

vTEMPIRTUR?,R1T.SP('IINSIVE SWITCH HAVING SELF-CONTAINED HEATER Filed Feb. 16, 1967 FIG. Z

INVENTORS: WILL/AM R. -DAL/EA/Pdf EL new 7'. pave-Ammer BY 75,- .f Ml- ATTORNEYS United States Patent O 3,474,372 TEMPERATURE-RESPONSIVE SWITCH HAVING SELF-CONTAINED HEATER William R. Davenport, Bricktown, and Elmer T. Davenport, Point Pleasant, NJ., assignors to Crowell Designs Inc., a corporation of New Jersey Filed Feb. 16, 1967, Ser. No. 616,586 Int. Cl. H01h 37/52 U.S. Cl. 337-1 2 Claims ABSTRACT OF THE DISCLOSURE A temperature-responsive switch, closed-when-cool, open-when-warm, is surrounded by a constantly energized electrical heater winding. The switch remains open when not contacted by the liuid, eg., water, to be detected. Electrical apparatus, e.g., a bilge pump, is connected to a source of power via the switch. When iluid contacts the switch, the latter is cooled and closes, and apparatus is energized.

This invention relates to a device for detecting the presence of a particular fluid at a certain point in an enclosure, and controlling the operation of an electrical apparatus in response to such detection.

It is an object of the invention to provide a device of simple, yet reliable, construction capable of detecting the interface between two different fluids, e.g., a gas and a liquid, and initiating the operation of an apparatus in response thereto.

It is another object of the invention to provide such a device which is corrosion-resistant, and has a long useful life.

The invention comprises, in brief, a temperature-responsive switch built so that its contacts are closed when cool and open when warm. The switch is connected in a circuit between a power source and an apparatus to be controlled. A constantly energized electric heater surrounds the switch and elevates its temperature sufficiently to maintain the contacts separated, and hence the apparatus deenergized. When the fluid to be detected touches the switch and draws away suicient heat to reduce the switch temperature below its critical value, the switch closes and the apparatus begins operating.

The switch and heater are preferably encapsulated in glass or a plastic so that the fluid being detected can have no deleterious effect on these components. In addition, the heater preferably includes high and low heat portions, the high heat portion being energized only during the periods of operation of the apparatus, to rapidly raise the temperature of the switch, and cause it to open should no fluid be detected by the switch.

The invention will be described in more detail below with reference to the accompanying drawings.

In the drawings:

FIG. 1 is a fluid detection device according to this invention; and

FIG. 2 is a schematic circuit diagram indicating how the device may be employed.

The present invention may include any suitable type of temperature-responsive switch. For example, in the device chosen to illustrate the present invention, a switch of the type made by Metals & Control Inc., a subsidiary of Texas Instruments Incorporated, and Sold under the trademark Klixon, may be employed. These switches are referred to as Miniature Snap-Acting Protectors 9700 Series.

As shown in FIG. 1, such a switch includes a stationary contact and a movable contact 11. The stationary contact 10 is a silver strip mounted on a metal support 12, which itself is mounted or an insulator 3,474,372 Patented Oct. 21, 1969 block 13. The movable contact 11 is a silver button secured to a snap-acting disk 14. Such a disk is wellknown and has a circular or oval shape when viewed face-on, and is dished. Thus, as viewed in FIG. 1, when the switch is cool, the upper face of disl. 14 is convex and the lower face is concave. When the disk is heated, it does not gradually change shape, as is true of an ordinary bi-metallic strip. Instead, when its critical temperature is reached, the disk suddenly snaps into a new position wherein its lower face is convex and its upper face is concave. As a result of this reaction, the contacts 10 and 11 are separated. Thus, it will be seen that this switch is made to be closed when cool and open when warm.

The end of the disk 14 opposite the contact button 11 is sandwiched between the arms of a U-shaped bend in a metal terminal 15. The terminal 15 and contact 10 are separated by a ceramic insulator 18, and the entire assembly is enclosed within a metal housing 19. A conductor 20 engages the contact 10, and a conductor 21 engages the terminal 15, these conductors extending out of the open end of the housing 19, and being covered by insulation 22. The conductors are separated by an insulation member 24.

According to the present invention, an electric heater 23 is provided, in the form of a high resistance wire wound around the housing 19, One end of the winding 23 is connected t0 the conductor 20, and the other end is connected to the conductor 21. The winding 23 is tapped at some point along its length, and conductor 26 is connected to the winding at the tapped point, the conductor having insulation 27. To make the entire switch assembly resistant to corrosion which might be caused by the Huid which the switch is intended to detect, it may 4be completely encapsulated in a suitable material 28, such as an epoxy resin, or glass. The material 28 covers part of the insulation 22 and 27, so that only the insulation covered conductors extend from the encapsulation.

The detection device of the present invention is obviously useful in a wide variety of environments. However, for the sake of illustration, its use will be described in connection with controlling the operation of a bilge pump, .e., a pump employed to remove water which accumulates in the bilge of a boat. FIG. 2 shows the switch connected in a circuit for controlling the motor 25 of a bilge pump. Power for running the motor is supplied by a battery 29, one terminal of which is connected to ground via a conductor 30. The other terminal of the battery is connected to a manually operable selector switch 31. If the switch is moved into engagement with the contact 34, a circuit will be completed from the battery, 4through switch 31, and conductor 20, and motor 25, for manually controlling the operation of the motor. On the other hand, if the switch is swung into engagement with contact 35, the circuit will be set for automatic operation of the pump motor 25.

The 4broken line in FIG. 2 represents the encapsulation material 28, and the encapsulated detection device is mounted in the bilge, possibly on the pump housing, at an appropriate location to be covered with water when a significant amount of water accumulates in the bilge. With the switch 31 in'engagement with the contact 35, a circuit is completed from the battery 29, through conductor 21, temperature-responsive switch 10, 11, conductor 20, and motor 25, to initially actuate the pump, regardless of whether or not there is water in the bilge. A circuit is also completed from the battery, through switch 31, conductor 21-, the low heat portion 36 of heater 23, and conductor 26. Additionally, a circuit is completed from the battery, through switch 31, conductor 21, switch 10, 11, high heat portion 37 of heater 23, and conductor 26. The connection of con- 3 ductor 26 to the winding 23 is such that the portion 36 is longer than the portion 37, and hence has more resistance and produces less heat.

With both heater portions 36 and 37 active, the temperature-responsive switch heats up quickly, and the contacts and 11 separate. Consequently, the motor 25 stops running, and the heater portion 37 is deenergized. The heat developed by the heater portion 36 is capable of maintaining the temperature of the switch high enough to keep the contacts 10 and 11 separated. As long as the bilge remains dry, therefore, the pump remains inactive. When water in the bilge rises and surrounds the detection device, the temperature of the device drops because the water conducts heat from the device faster than does the air which otherwise surrounds it. As a result, the contacts 10 and 11 close, and the pump motor 25 runs. When the bilge is empty of water again, the winding 23 quickly heats up the switch, and the contacts 10 and 11 open.

Although it is believed that the invention will be understood from the foregoing description, the following example of a specific detection device may prove helpful. The following values are given only for purposes of illustration, and are not intended to limit the scopeof the invention. A temperature-responsive switch of the type described above, and built to open at a temperature of 167 F. and close at a temperature of 131 F., was wound with No. 32 nickel-chromium alloy wire, the wire being insulated. The portion 36 of the winding was 6.85 feet long and had a resistance of 72 ohms, and the portion 37 was 2.28 feet long and had a resistance of 24 ohms. When used with a 12 volt battery 29, the portion 36 developed 2 watts, and the portion 37, 6 watts. With the switch 31 engaging contact 35, it `was found that the contacts 10 and 11 remained open even when the air temperature dropped to 25 F. On the other hand, the contacts 10 and 11 closed when the device was surrounded by water at 92 F.

It will be appreciated that the specific arrangement delined above may be varied to suit the particular circumstances of the environment in which the device is used. For example, the point at which the winding 23 is tapped for the connection of conductor 26 may be varied, and if desired, two separate windings may be used to form the high and low heat portions, 37 and 36, ofthe heater 23.

The invention has been shown and described in preferred form only, and by way of example, and many variations may be made in the invention which will still be comprised within its spirit.v AItis understood, therefore, that the invention is not limited to any specific form or embodiment except insofar as such limitations are included in the appended claims.

A What is claimed is:

1. A device for detecting the presence of a particular uid at a certain point within an enclosure and controlling the operation of an electrical apparatus in response torsuch detection, comprising a temperature-responsive switch between a source of power and the apparatus, said switch being closed when relatively cool and open `when relatively warm, electrical heating means adjacent to said switch and connected in parallel with it, said heating means serving to elevate the temperature of said switch to keep it open when it is out of contact with the fluid, whereupon the apparatus is deenergized, said switch becoming relatively cool and closing when contacted by said fluid, whereupon the apparatus is connected to the power source, and a heat-conductive housing enclosing said switch, said heating means comprising a resistance wire wound around said housing and including a relatively high resistance-low heat section, and

. a` relatively low resistance-high heat section, said high resistance section being connected constantly across said power source -when said device is in operation, and said low resistance section being connected in series with said switch across said power source.

2. A device as defined in claim 1 wherein said high and low resistance sections are portions of a single winding.

References Cited BERNARD A. GILHEANY, Primary Examiner R. L. COHRS, Assistant Examiner Us. C1. X.R. 337-100, 102, 112, 372, 38o, 

